Development of a microtiter plate version of the yeast DEL assay amenable to high-throughput toxicity screening of chemical libraries

The yeast plate-based deletion (DEL) assay has been previously shown to detect a wide range of carcinogens. Of 60 compounds of known carcinogenic activity, 92% were correctly detectable with the DEL assay whereas 62% were correctly detectable with the Ames assay [W.W. Ku, J. Aubrecht, R.J. Mauthe, R.H. Schiestl, A.J. Fornace Jr., Why not start with a single test: a transformational alternative to genotoxicity hazard and risk assessment, Toxicol. Sci. (2007)]. In this manuscript we describe a modification of the yeast DEL assay into a colorimetric assay using the MTS tetrazolium compound (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) to allow for efficient detection of chemical genotoxicity. It has been micro-scaled and can be performed in 96- or 384-well format. Chemicals previously characterized with the DEL plate-based assay were utilized to test the new well-based format, and a group of cross-linking agents, previously uncharacterized by the DEL assay, were scored for genotoxicity using this new assay format. These compounds induced a range of genotoxicity detectable with the well-based DEL assay, and a lack of sensitivity was found only at extremely low genotoxic levels determined by the plate-based DEL assay. We suggest this new well-based version of the DEL assay can be used as an economical alternative to the plate-based assay to screen large numbers of compounds, such as chemical libraries in a high-throughput screening setting.